Water based polymer emulsions (latex emulsions) are susceptible to microbial contamination resulting in product spoilage. Polymer emulsions are dispersions of fine organic polymer particles in water. These polymer particles are suspended and stabilized in an aqueous environment with additional organic substrates, such as surfactants and protective colloids. Surfactants, protective colloids, such as poly(vinyl alcohol) and hydroxyethyl cellulose, thickeners and other additives, and the polymer itself all provide a supply of carbon nutrition for microorganisms to metabolize. Polymer emulsions are therefore susceptible to spoilage due to microbial attack and propagation. Standard industrial practices combat such product biodeterioration by the addition of various industrial biocides (antimicrobial agents) directly after the manufacturing process. Examples of commonly used industrial biocides are: 1,2-benzisothiazolin-3-one (BIT), and a blend of 5-chloro-2-methyl-4-isothiazolin-3-one (CIT) and 2-methyl-4-isothiazolin-3-one (MIT). Examples of other biocides commonly used for polymer emulsion preservation include 1,2-dibromo-2,4-dicyanobutane (DBDCB), 2,2-dibromo-3-nitrilo-propionamide (DBNPA), 2-bromo-2-nitro-1,3-propanediol (BNPD), aldehyde derivatives, formaldehyde releasing agents, hydantoins, and chlorinated aromatics.
These commonly used biocides are usually adequate to preserve various types of polymer emulsions against most industrial spoilage from bacteria and fungi. However, polymer emulsions are more susceptible to spoilage by certain types of microbes. For example, biodeteriogenic microbes that can survive in acidic environments and/or that metabolize alcohols, such as Gluconoacetobacter liquefaciens (GABL), have begun to emerge and thrive in polymer emulsions, even in the presence of commonly used industrial biocides. Biodeteriogenic microbes include bacteria and fungi that can adversely affect the commercial value of products and materials. Some biodeteriogenic microbes have become so well adapted to the environment present in these emulsions that the standard industrial biocides are inadequate to prevent product spoilage over the entire product shelf life; e.g., 6 to 12 months. A significant rise in polymer emulsion biodeterioration problems has resulted in a need to identify more effective preservative systems.
It is known that VOC's (volatile organic compounds) in polymer emulsions exert some level of a bacteriostatic, it not bacteriocidal, effect, which can inhibit the growth of biodeteriogenic microbes. Examples of VOC's present in polymer emulsions are unreacted monomers, such as vinyl acetate, acetic acid, methanol, acetaldehyde, and formaldehyde. Recent developments in polymer emulsion technology, in response to regulatory issues and environmental concerns, have lead to reductions in residual VOC. Such VOC reductions impact polymer emulsions in many ways from a microbiological perspective. For example: 1) it creates an emulsion environment more conducive to microbial growth, 2) it may permit the emergence of new microorganisms that find the new emulsion environment more hospitable, 3) it poses additional challenges to current preservative technologies, and 4) it creates the need for new preservation methods to prevent biodeterioration over the product's shelf life.
Although there are a significant number of biocides that can kill microorganisms effectively and can provide very good preservation for polymer emulsions and other industrial products, only a limited number of these exhibit acceptably low toxicity to higher organisms, e.g., humans. The choice of effective biocides that can be added to polymer emulsions becomes even more limited when United States Food and Drug Administration (FDA) clearances are required for the polymer emulsion end use. Many polymer emulsions are used to manufacture consumer goods, such as adhesives and papers for food packaging, diapers, paper towels, baby wipes, and feminine hygiene products. As a result of such contact with skin and indirect contact with foods, the polymer emulsions used in these applications must have the appropriate FDA clearances. These FDA clearances are based on favorable toxicological profiles, including no skin sensitization. In order for a polymer emulsion to receive the necessary FDA clearances, all of its constituents, including the preservative technology, must meet FDA's rigorous toxicological criteria when used at concentrations required for satisfactory performance in the polymer emulsion. FDA-approved biocides have use level restrictions. In some cases, the minimum biologically effective concentration is greater than the maximum allowable use level. Typically, this results in premature product biocontamination and biodeterioration. Additionally, microorganisms continue to evolve and new microorganisms are beginning to appear that exhibit resistance to some of the more common industrial biocidal agents, particularly at the allowable use level. A tightening regulatory environment, specific consumer good manufacturing specifications, public concern, and product liability further complicates biocide selection and use. For example, isothiazolinones are widely used antimicrobial agents for many consumer products, but their known skin sensitization property causes concern among many consumer goods manufacturers. Such health concerns and microbial resistance are leading to a search for preservation alternatives and new preservation approaches. Cationic compounds, such as quaternary ammonium compounds, are well known in the antimicrobial art and are widely used as disinfectants for surfaces. For example, they are used to disinfect floors, walls, countertops, equipment surfaces, food contact surfaces, and the like in hospitals, schools, nursing homes, restaurants, and residential homes. Furthermore, combinations of detergents with cationic compounds are widely used formulations for cleaning and disinfecting or sanitizing such surfaces with a single product. Cationic compounds are also used to inhibit the growth of algae and microorganisms in water, such as in swimming pools. Cationic compounds have been utilized on a limited basis for the preservation of industrial products and to prevent microbial growth in aqueous systems.
Examples of uses of cationic compounds in disinfectant compositions and in preservatives for polymer emulsions are discussed below:
U.S. Pat. No. 6,066,674 (Hioki et al., 2000) teaches a germicidal-disinfectant detergent composition composed of a cationic germicide, a metal chelating agent, and at least one surfactant selected from anionic, nonionic, and amphoteric surfactants. Metal chelating agents, such as sodium EDTA, sodium citrate, and sodium tripolyphosphate, are reported to be necessary to maintain germicidal activity of the cationic species in the presence of anionic surfactants.
US 2002/0099113 A1 (Rabasco et al., 2002) teaches a method of preserving colloid-stabilized polymer emulsions against microbial attack and spoilage using selected cationic compounds. It is also directed to compositions containing colloid-stabilized polymer emulsions and cationic compounds that are resistant to contamination with biodeteriogenic microbes. The polymer emulsions contain little or no nonionic or anionic surfactants and little or no anionic constituents.
U.S. Pat. No. 6,383,505 B1 (Kaiser et al., 2002) discloses an antimicrobial lotion for topical use which comprises an oil-in-water emulsion with a dispersant of emollient droplets in an oil phase and an antimicrobial agent in a water phase. It is reported that a combination of anionic and nonanionic surfactants stabilize the emulsion and maintain a cationic antimicrobial agent primarily in the water phase.
A need remains for a method of protecting polymer emulsions against product biodeterioration by microbes, especially polymer emulsions stabilized with surfactants and/or containing anionic constituents, and those with low VOC's.